1. Field of the Invention
The present invention relates to a communications network and in particular to a circuit-switched network such as an ATM (Asynchronous Transfer Mode) network.
2. Related Art
Conventionally, networks using packet-based protocols such as Internet Protocol (IP) have functioned on a best effort basis. As a result, quality of service, as measured by such parameters as packet loss and latency, has varied considerably depending on the loading of network resources such as routers. While such variation is acceptable for some applications, such as Email, it is potentially a barrier to the use of Internet Protocol for more critical applications such as voice telephony or multimedia conferencing. Accordingly, considerable effort has been directed to providing improved Quality of Service (QoS). One approach has been to supplement IP with QoS-related protocols such as ReSource reserVation Protocol (RSVP). Another approach has been to make use of circuit-switched networks, and particularly ATM networks to carry IP traffic. When a customer terminal and a data source are both connected to an ATM network, then a Switched Virtual Circuit (SVC) may be used to “cut-through” from the terminal to the source, bypassing any intermediate routers, and providing a uniform and predictable QoS level. However, establishing a switched virtual circuit is a complex operation requiring the setting of a number of service parameters and this presents a barrier to the widespread adoption of this technique, despite its advantages.
The paper by W Almesberger et al, “Guaranteeing Quality of Service for the Web using ATM”, Data Highway, 1 Jan. 1995, pages A21/1-A21/16 describes an attempt to automate the process of establishing connections over an ATM network. The information required to establish the connection is split between the user agent field defined in the HTTP (hypertext transport protocol) and metadata encoded with the HTTP document. This complex approach requires two ATM connections to be established, and several signalling messages to be exchanged. Such a signalling overhead is undesirable since it increases the time required to switch to the ATM network, and hence reduces the transparency of the change between networks to the user. It also places additional demands on the network resources.